Use of indefinite article with relative clause

Question

I posted a question quite long time ago asking whether "that was a day that my dog died" is valid. The answers said "no!", telling that a dog cannot die twice.

I thought it was possible, for I thought I was introducing an item for the fist time, for which the indefinite article is necessary.

So I searched around and found this sentence: "this is a book I told you about yesterday."

The answerer was saying that "it might suggest that it was one of several books, or it might mean that you don't think I remember it", which is similar to introducing an item for the first time, because the listener does not have any information about it due to inability to remember it.

But some others said that "this is a book I told you about yesterday can only be sensibly used when the book is one of several that I told you about. Whether I think you remember or not is irrelevant."

So I came to this conclusion:

When a noun modified by a relative clause is used, the indefinite article is used only for the situations in which the noun is one of several.

I was naively happy with the satisfaction that I cleared up some confusion. Yet it occurred again, when I found that:

A woman who fell 10 meters from High Peak was lifted to safety by a helicopter.

is actually valid, even though there was only one woman who fell 10 meter from High Peak (it would be strange if there were more than one).

And more surprising was that the reason for its validity was because it was introduced for the first time, news they said. "This is news. We haven't heard about this woman before."

Here is the question: https://english.stackexchange.com/questions/265002/using-the-in-adjective-relative-clause

So I just cannot see the difference between "this is a book I told you about yesterday" and "a woman who fell 10 meters from High Peak was lifted to safety by a helicopter."

Why can a definite article be used with "woman" for introducing for the first time and not with "book"?

Also, these two uses puzzled me even further.

“Everywhere there is growing interest in the Exposition,” he told Burnham in a June 20 letter from Biltmore.

It should be "the" according to the explanation people have given me, right? Unless there is more than one letter he sent to Burnham on June 20, which is unlikely.

While aboard the train, Burnham wrote a letter to Olmsted that contained a less-than-candid description of the meeting with the architects.

Likewise, it should be "the" unless Burnham wrote several letters that contained a description of the meeting.

I fail to notice how this "letter" is different from "day". There was only one letter as there was only one day that my dog died. So why indefinite article cannot be used with "day" as used above?

It became a rather long question.

However, my central question is, what controls the use of the definite and indefinite article when modifying a noun with relative clause?

Answer 1

I think it all comes down to what the writer/speaker thinks about the reader/listener

ie. If it is new to the reader use 'a', otherwise use 'the'

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as for your examples

So I just cannot see the difference between "this is a book I told you about yesterday" and "a woman who fell 10 meters from High Peak was lifted to safety by a helicopter."

Why can a definite article be used with "woman" for introducing for the first time and not with "book"?

If you told me about the book yesterday, then it wouldnt be new information so it would be: "this is the book i told you about yesterday", Using 'a' in this case almost implies that I forgot about it, and you are reminding me

For the second one, I have never heard of the[1] woman (in the article) before so you describe her as 'a' woman and not 'the' woman.

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the[1] last examples:

It should be "the" according to the explanation people have given me, right? Unless there is more than one letter he sent to Burnham on June 20, which is unlikely.

This does read to me as if there is more than one or that he wrote so many letters over the years that they can only specify which one they are talking about by date.

Likewise, it should be "the" unless Burnham wrote several letters that contained a description of the meeting.

it is 'a' because he wrote only one letter. "Burnham wrote one letter to Olmsted...", if you said 'the' in this case, it would imply that I knew about the letter before you said the sentence

[1] I use 'the' because you know what I'm refering to here

Answer 2

I think the some of the answer revolves around the assumption of prior knowledge we make of the listener. We choose a form of words that is politely appropriate for the listener's assumed knowledge - note that this does not actually necessitate that this really is what the listener knows.

Situation: I spoke to the listener yesterday, we spoke about one book, he recommended the book to me, I'm pretty sure that he will remember the conversation.

This is the book we spoke about yesterday.

Situation: I spoke to the listener yesterday, we spoke about many books, although he may remember the entire conversation he cannot know which particular book I'm holding:

This is a book we spoke about yesterday

Situation: A woman has fallen. This is a news program, we have no reason to suppose that our listeners know this particular woman. We cannot say

The woman has fallen

the listener has no point of reference, in fact the woman's effective identity is that she fell and was rescued

a woman who fell ...

The letters work in the same way. We the listener have never seen the letters, have no point of reference, if we said "the letter" they would feel that we are assuming knowledge they have yet to receive. So we say "a letter" and then clarify by reference to the content

XXX wrote a letter, which ...

Note. If we were in a museum and could see the letter our guide might say:

Look at this letter written by X on Date.

we now have our point of reference, so he can now say

The letter ...

Your original example is slightly more subtle

This was the day my dog died

We use the because we are immediately going to give a very specific point of reference.

We could do something similar for dramatic effect with the letter

While aboard the train, Burham wrote the fateful letter.

In effect we are playing a game with the listener, he knows that we haven't given him the full point of reference, but we have given him information that some very specific detail will be coming shortly.

this was the day (... dramatic tension ...) my dog died

Answer 3

In the examples of the letters, in each case the description of the letter (written on that date, containing that account) is, at least in grammar, subordinate to the mention of the letter's existence, which is new and thus has ‘a’ rather than ‘the’. You could split the sentence in two:

Burnham wrote a letter to Olmsted. The letter contained ...

But you would not say

That was a day. My dog died on the day.

... partly because the existence of the day is not news to the listener.